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Technical Note: Single time point dose estimate for exponential clearance
Journal article   Open access   Peer reviewed

Technical Note: Single time point dose estimate for exponential clearance

Mark T Madsen, Yusuf Menda, Thomas M O'Dorisio and M. Sue O'Dorisio
Medical physics (Lancaster), Vol.45(5), pp.2318-2324
05/2018
DOI: 10.1002/mp.12886
PMCID: PMC5948162
PMID: 29577338
url
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5948162View
Published (Version of record) Open Access

Abstract

Objective Although personalized dosimetry may be desirable for radionuclide therapy treatments, the multiple time samples required to determine the total integrated activity puts a burden on patients and clinic resources. The aim of this paper is to demonstrate that when some prior knowledge is known about the tracer kinetic parameters, the total integrated activity (and thus radiation dose) can be estimated from a single time sample. Methods Mathematical derivations have been performed to generate equations for the total integrated activity in terms of a single time sample of activity for monoexponential and biexponential clearance. Simulations were performed using both exponential models where the rate constants and associated parameters were randomly sampled from distributions with a known mean. The actual total integrated activity for each random sample was compared with the estimated total integrated activity using the mean value of the parameters. Retrospective analysis of 90Y DOTATOC data from a clinical trial provided a comparison of actual kidney dose with the estimated kidney dose using the single time point approach. Results The optimal sampling time for the single point approach was found to be equal to the mean time of the rate constant. The simulation results for the monoexponential and biexpoential models were similar. Regressions comparing the actual and estimated total integrated activity had very high correlations (r2 > 0.95) along with acceptable standard errors of estimate, especially at the optimal sampling point. The retrospective analysis of the 90Y DOTATOC data also yielded similar results with an r2 = 0.95 and a standard error of estimate of 61 cGy. Conclusions In situations where there is prior knowledge about the population averages of kinetic parameters, these results suggest that the single time point approach can be used to estimate the total integrated activity and dose with sufficient accuracy to manage radionuclide therapy. This will make personalized dosimetry much easier to perform and more available to the community.
 personalized radionuclide therapy single sample time radiation dose estimate exponential clearance

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